Method of treating coal and product thereof



Patented Jan. 30, 1934 METHOD OF TREATING COAL AND PRODUCT THEREOF Nathaniel R. Landon, Mount Kisco, and Ernest Victor Collins, Jr., Brooklyn, N. Y., assignors to Delaware, Lackawanna & Western Coal Company, New York,

New Jersey N. Y., a corporation of No-Drawing. Application February 14, 1930 I Serial No. 428,511

7 Claims.

This invention relates to the treatment of coal that has become discolored either in storage or below the surface to restore essentially the original appearance of bright black coal.

The consuming public, who are accustomed to recognize anthracite coal by its jet black color and luster often assume that coal which is dull or discolored and has thus lost its characteristic appearance is poor in quality. Coal that has 0 become discolored cannot be restored to its original jet black appearance by ordinary washing. Consequently serious losses are sustained by the producer because this dull or discolored coal does not command the price of coal that is black and bright in appearance although analysis indicates that the change is only one of appearance and there is no loss of fuel value or consequential change in chemical composition.

It is the object of the present invention to pro- .vide a practical method of treating discolored coal to restore its original characteristic appearance.

The iron in the mineral matter of coal is considered to be almost wholly present in combination with sulphur. Under the influence of atmospheric exposure or subjected to mildly acid mine water, the iron sulphides become oxidized presumably to insoluble basic sulphates, oxides and other compounds imparting to the coal a rusty appearance. Other reactions go on and other metallic compounds may show on the surface. This is particularly true of storage coal and consequently the longer it is exposed to atmospheric influences or acid water, the greater becomes the discoloration.

We have discovered that the original appearance of discolored coal can be restored by treating the coal under appropriate conditions with tanning materials in general. The term tanning .materials as here used includes a variety of reagents which combine with iron compounds and when oxidized produce bleach compounds on the surface of the coal. Among such reagents are tannin or tannic acid, gallic acid, pyrogallic acid or pyrogallol and extracts such as quebracho, chestnut, cutch, divi-divi, gambier, myrobolans, nutgalls, sumac, valonia, hemlock, spruce, oakbark, Wattle and the like. We have also discovered that extract of logwood may be applied advantageously to discolored coal either alone or "in combination with one or more of the tanning materials mentioned.

As an example of the method we may proceed as follows: a 5% solution by weight of gallic or pyrogallic acid is heated, preferably to approximately 180 F. The discolored coal is immersed in this solution for a period sufficient to accomplish the object, usually about one minute, after which the coal is removed on a slow con.- veyor in which the coal is exposed to the atmosphere so that the solution dries on the coal and the iron compounds formed with the reagent used are oxidized. We have found that the best results are secured if the solution is maintained in a slightly alkaline condition. A suitable alkali such as sodium carbonate can be added in proportions to maintain the acid condition.

As another example we may employ a 20% solution by weight of sumac at approximately 180 F. The coal is introduced to a tank containing this solution and is permitted to remain therein for about 45 seconds. It is withdrawn by a conveyor moving at a slow rate to permit drying and oxidation.

We prefer to immerse the coal in the solution, but the solution can be sprayed or applied otherwise to the coal, so long as the discolored coating is saturated with the reagent. The excess solution which is drained from the coal can be returned and reused.

As hereinbefore indicated, we may employ similarly an extract of logwood in solution with or without the addiiton of one or more of the reagents mentioned.

Coal which has been treated as hereinbefore described presents the characteristic appearance of freshly mined coal. The losses heretofore incident to the storage of coal and consequent discoloration thereof are avoided by the application of the simple and effective procedure described.

The term tannins as used in the accompanying claims includes the reagents hereinbefore mentioned and their equivalents. Equivalent reagents are such as may react with iron compounds on the surface of the coal to produce a black coating.

Various changes may be made in the details of operation and in the reagents employed without departing from the invention or sacrificing any of the advantages thereof.

We claim:

1. The method of treating coal which is discolored by oxidized iron compounds which oomprises subjecting the coal to the action of a tannin solution and exposing the coal thereafter to the atmosphere whereby the oxidized iron compounds are converted into other compounds which restore the natural appearance of the coal.

2. The method-of treating coal which is discolored by oxidized iron compounds which comprises subjecting the coal to a solution contain-' ing a reagent of the group consisting of tannic acid, gallic acidand pyrogallic acid and exposing the coal thereafter to the atmosphere whereby the oxidized iron compounds are converted into other compounds which restore the natural appearance of the coal.

3. The method of treating coal which is dis colored by oxidized iron compounds which comprises subjecting the coal to a solution of an extract containing a reagent of the group consist 5. The method of treating coal which is dis: colored by oxidized iron compounds to restore the natural appearance thereof which comprises converting the iron compounds into black compounds byrreaction with a tannin.

6. The method of treating coal which is discolored by oxidized iron compounds which comprises treating the coal with an extract of logwood and exposing the coal thereafter to the atmosphere whereby the oxidized ironicompounds are converted into other compounds which restore the natural appearance of the coal.

7. The method of treating coal which is discolored by oxidized iron compounds which oomprises treating the coal with an extract of logwood and a tannin and exposing the coal thereafter to the atmosphere whereby the oxidized NATHANIEL R. LANDON. ERNEST VICTOR COLLINS, JR. 

